274 research outputs found
Ce3+, Eu2+ and Mn2+-activated alkaline earth silicon nitride phosphors and white-light emitting LED
The invention refers to an alkaline earth silicon nitride phosphor of the MSiN2 type that is activated by Ce3+ and/or Eu2+ and/or Mn2+ ions. A preferred embodiment of the phosphor is defined by the general formula MSiN2:A, wherein M is a divalent metal ion, especially Mg, Ca, Sr, Ba, Be and/or Zn, and A is an activator chosen from the group Ce3+, Eu2+ and/or Mn2+. A preferred application for this phosphors is a white-light emitting LED using the phosphor for conversion of radiation
Ce3+, Eu2+ and Mn2+-activated alkaline earth silicon nitride phosphors and white-light emitting LED
The invention refers to an alkaline earth silicon nitride phosphor of the MSiN2 type that is activated by Ce3+ and/or Eu2+ and/or Mn2+ ions. A preferred embodiment of the phosphor is defined by the general formula MSiN2:A, wherein M is a divalent metal ion, especially Mg, Ca, Sr, Ba, Be and/or Zn, and A is an activator chosen from the group Ce3+, Eu2+ and/or Mn2+. A preferred application for this phosphors is a white-light emitting LED using the phosphor for conversion of radiation
Cavity QED and quantum information processing with "hot" trapped atoms
We propose a method to implement cavity QED and quantum information
processing in high-Q cavities with a single trapped but non-localized atom. The
system is beyond the Lamb-Dick limit due to the atomic thermal motion. Our
method is based on adiabatic passages, which make the relevant dynamics
insensitive to the randomness of the atom position with an appropriate
interaction configuration. The validity of this method is demonstrated from
both approximate analytical calculations and exact numerical simulations. We
also discuss various applications of this method based on the current
experimental technology.Comment: 14 pages, 8 figures, Revte
Inhibiting decoherence via ancilla processes
General conditions are derived for preventing the decoherence of a single
two-state quantum system (qubit) in a thermal bath. The employed auxiliary
systems required for this purpose are merely assumed to be weak for the general
condition while various examples such as extra qubits and extra classical
fields are studied for applications in quantum information processing. The
general condition is confirmed with well known approaches towards inhibiting
decoherence. A novel approach for decoherence-free quantum memories and quantum
operations is presented by placing the qubit into the center of a sphere with
extra qubits on its surface.Comment: pages 8, Revtex
Topological quantization and degeneracy in Josephson-junction arrays
We consider the conductivity quantization in two-dimensional arrays of
mesoscopic Josephson junctions, and examine the associated degeneracy in
various regimes of the system. The filling factor of the system may be
controlled by the gate voltage as well as the magnetic field, and its
appropriate values for quantization is obtained by employing the Jain hierarchy
scheme both in the charge description and in the vortex description. The
duality between the two descriptions then suggests the possibility that the
system undergoes a change in degeneracy while the quantized conductivity
remains fixed.Comment: To appear in Phys. Rev.
Dynamically turning off interactions in a two component condensate
We propose a mechanism to change the interaction strengths of a two component
condensate. It is shown that the application of pi/2 pulses allows to alter the
effective interspecies interaction strength as well as the effective
interaction strength between particles of the same kind. This mechanism
provides a simple method to transform spatially stable condensates into
unstable once and vice versa. It also provides a means to store a squeezed spin
state by turning off the interaction for the internal states and thus allows to
gain control over many body entangled states.Comment: 7 pages 5 figures, symbols changed, minor changes, to appear in Phys.
Rev.
Effect of collective neutrino flavor oscillations on vp-process nucleosynthesis
The vp process is a primary nucleosynthesis process which occurs in core
collapse supernovae. An essential role in this process is being played by
electron antineutrinos. They generate, by absorption on protons, a supply of
neutrons which, by (n,p) reactions, allow to overcome waiting point nuclei with
rather long beta-decay and proton-capture lifetimes. The synthesis of heavy
elements by the vp process depends sensitively on the \bar{\nu}_e luminosity
and spectrum. As has been shown recently, the latter are affected by collective
neutrino flavor oscillations which can swap the \bar{\nu}_e and
\bar{\nu}_{\mu,\tau} spectra above a certain split energy. Assuming such a swap
scenario, we have studied the impact of collective neutrino flavor oscillations
on the vp-process nucleosynthesis. Our results show that the production of
light p-nuclei up to mass number A=108 is very sensitive to collective neutrino
oscillations.Comment: 4 pages, 3 figures, submitted to Physics Letters
Heating and decoherence suppression using decoupling techniques
We study the application of decoupling techniques to the case of a damped
vibrational mode of a chain of trapped ions, which can be used as a quantum bus
in linear ion trap quantum computers. We show that vibrational heating could be
efficiently suppressed using appropriate ``parity kicks''. We also show that
vibrational decoherence can be suppressed by this decoupling procedure, even
though this is generally more difficult because the rate at which the parity
kicks have to applied increases with the effective bath temperature.Comment: 13 pages, 5 figures. Typos corrected, references adde
Single Atom Cooling by Superfluid Immersion: A Non-Destructive Method for Qubits
We present a scheme to cool the motional state of neutral atoms confined in
sites of an optical lattice by immersing the system in a superfluid. The motion
of the atoms is damped by the generation of excitations in the superfluid, and
under appropriate conditions the internal state of the atom remains unchanged.
This scheme can thus be used to cool atoms used to encode a series of entangled
qubits non-destructively. Within realisable parameter ranges, the rate of
cooling to the ground state is found to be sufficiently large to be useful in
experiments.Comment: 14 pages, 9 figures, RevTeX
Self-Assembled Molecular-Electronic Films Controlled by Room Temperature Quantum Interference
If single-molecule, room-temperature, quantum interference (QI) effects could be translated into massively parallel arrays of molecules located between planar electrodes, QI-controlled molecular transistors would become available as building blocks for future electronic devices. Here, we demonstrate unequivocal signatures of room-temperature QI in vertical tunneling transistors, formed from self-assembled monolayers (SAMs), with stable room-temperature switching operations. As a result of constructive QI effects, the conductances of the junctions formed from anthanthrene-based molecules with two different connectivities differ by a factor of 34, which can further increase to 173 by controlling the molecule-electrode interface with different terminal groups. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting room-temperature on-off current ratio of the lowest-conductance SAMs can reach up to 306, about one order of magnitude higher than that of the highest-conductance SAMs
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